We are studying the effects of a double deficiency of choline and linolenic acid upon the lipids of brain, liver, muscle and plasma of rats. Evidence indicates that phosphatidylethanolamines (PE) which contain decosahexaenoic acid (22:6n3) are preferred precursors in the conversion of PE to phosphatidylcholines (PC or lecithins) in rats. Linolenic acid, 18:3n3, is an essential fatty acid and the precursor of 22:6n3. If 22:6n3 PE is an important precursor for choline biosynthesis in rats, then a dietary deficiency of 18:3n3, which causes a great decrease in 22:6n3 PE, should also reduce the endogenous formation of choline. A double deficiency of both choline and 18:3n3 should therefore intensify the usual symptoms of choline deficiency, including fatty infiltration of the liver and reduced plasma lipids. We are analyzing the lipids of liver, plasma, brain and muscle to determine how the double deficiency has influenced the amounts and fatty acid patterns of cholesteryl esters, PC, PE, triglycerides and other lipids. A rat liver microsome-plus-supernatant system will be used to determine whether choline will reduce the formation of PE. It has been reported that ethanolamine kinase is inhibited by choline, and this inhibition could lead to reduced PE formation. This mechanism may explain the increased amount of PE found in livers of choline-deficient rats.